There are a variety of known designs of bolt actions for rifles. A design objective of bolt actions is the precise alignment of a bolt face to a cartridge chamber to properly position the firing pin to strike the primer of a cartridge. To achieve precise and repeatable firing results during competition shooting, it is desirable to accurately secure the bolt mechanism in its proper position and keep it relatively immovable with respect to the cartridge and barrel during movement of the firing pin and the striking of the cartridge primer.
Moreover, due to the nature of high-powered rifles, the bolt mechanism is subjected to enormous stress as gas pressure caused by cartridge firing rapidly builds and expels the projectile from the barrel. In order to achieve precise accuracy during firing, it is critical that the axis of the bolt and the firing pin remain parallel with the axis of the bore of the firearm barrel while also providing a perpendicular surface to accept a cartridge head.
In competition shooting, rimfire cartridges are often used with a bolt action rifle. The forces generated by a rimfire cartridge are much less than a center fire cartridge. A rimfire cartridge, when fired, is traveling about a third of the speed of a center fire cartridge which means the bullet is in the barrel a longer period of time when compared to a center fire. The resulting lag time in the barrel exposes the bullet to vibrations created during the firing process and these vibrations affect the bullet's trajectory. It has been proven through extensive testing that a front lock-up bolt design generally used with center fire ammunition accentuates the vibrations experienced by rimfire cartridges due to the close proximity of the lugs to the case rim and the lag time, and is therefore considered detrimental to accuracy.
In addition, known rear lock-up bolt receivers distribute bolt pressure over a maximum of two contact points at the rear of the receiver. This results in the bolt assembly flexing and moving during the firing of a round. Such movement of the bolt assembly also prevents consistent positioning of the components of the bolt action thereby jeopardizing accurate, repeatable performance by the shooting competitor.
Bolt action rifles that fire rimfire cartridges incorporate an offset firing pin. A center fire cartridge has a replaceable primer located in the center of the cartridge and when struck by the centrally located firing pin, the primer creates a flash that ignites the gun powder. In contrast, a rimfire cartridge's primer is part of the case. More specifically, there is a fold of brass material at the rim of the rimfire cartridge that has a chemical compound applied to the area inside the case prior to the gun powder and bullet being installed in the cartridge. The firing pin of a rimfire bolt action assembly is offset and strikes the rimfire cartridge on the outer edge of the case. Due to the firing pin being off center, the bolt will experience a force that is shifted to one side and the bolt will move away from the force if not supported properly.
Accordingly, there exists a need for a rear lock-up rimfire bolt action assembly that can evenly distribute the forward pressure the bolt assembly places on a chambered round and will not allow the bolt assembly to move or flex within the action body during the firing of the round.